Edge Evaluation Techniques for Graphics Hardware

1. A graphics processing unit comprising: two edge evaluation circuits; and a sequencer, coupled to the two edge evaluation circuits, including; a plurality of buffers; and a multiplexor, coupled between the plurality of buffers and the two edge evaluation circuits, to input from the plurality of buffers a first edge of a given primitive to a first of the two edge evaluation circuits and a second edge of the given primitive to a second of the two edge evaluation circuits in parallel with the first edge, and to input from the plurality of buffers a third edge of a given primitive to the first of the two edge evaluation circuits and a third edge of the given primitive to the second of the two edge evaluation circuits in parallel with the third edge and wherein the third and fourth edges are input in series to the first and second edges if the given primitive includes three or more edges.

2. The graphics processing unit of claim 1 , wherein each edge evaluation circuit computes an edge equation for a given edge.

3. The graphics processing unit of claim 1 , wherein each edge evaluation circuit computes an edge equation for an evaluation tile.

4. The graphics processing unit of claim 1 , wherein the two edge evaluation circuits are coupled in parallel with each other to the sequencer.

5. The graphics processing unit of claim 1 , wherein the first and second edges are input during a first clock cycle.

6. The graphics processing unit of claim 1 , wherein if the given primitive includes three or more edges the third and fourth edges are input during a second clock cycle.

7. The graphics processing unit of claim 1 , wherein the sequencer consumes less power than the two edge evaluation circuits.

8. The graphics processing unit of claim 1 , wherein the sequencer consumes less area on an integrated circuit die than the two edge evaluation circuits.

9. The graphics processing unit of claim 1 , wherein the two edge evaluation circuits are larger circuits than the sequencer.

10. An edge evaluation method comprising: buffering a plurality of edges of a given primitive; determining a number of edges of the given primitive to be evaluated; multiplexing a buffered first edge and a buffered second edge of the given primitive in parallel to a first edge evaluation circuit and a second edge evaluation circuit respectively, and sequentially multiplexing a buffered third edge and a buffered fourth edge of the given primitive in parallel to the first edge evaluation circuit and the second edge evaluation circuit respectively; evaluating in parallel the first edge by the first edge evaluation circuit and the second edge of the given by the second edge evaluation circuit and sequentially evaluating in parallel the third edge by the first edge evaluation circuit and the fourth edge by the second edge evaluation circuit if three or more edges are to be evaluated; and evaluating in parallel the first edge by the first edge evaluation circuit and the second edge by a second edge evaluation circuit if two or less edges are to be evaluated.

11. The method according to claim 10 , wherein evaluating each edge comprises computing an edge equation for each edge.

12. The method according to claim 11 , wherein the edge equation is computed for a given evaluation tile.

13. The method according to claim 10 , wherein a given edge is not evaluated if it is trivially already known.

14. A method comprising: buffering a plurality of edges of a given primitive to be evaluated; determining a number of edges of the given primitive to be evaluated; multiplexing a buffered first edge to a first edge evaluation circuit and a buffered second edge to a second edge evaluation circuit during a first clock cycle; and multiplexing a buffered third edge to the first edge evaluation circuit and a buffered fourth edge to the second edge evaluation circuit during a second clock cycle if three or more edges are to be evaluated.

15. The method according to claim 14 , wherein each edge evaluation circuit computes an edge equation.

16. The method according to claim 15 , wherein the edge equation is computed for a given evaluation tile.

17. The method according to claim 14 , wherein a given edge is not evaluated if it is trivially already known.